Cold drawn film made of an olefin polymer blend composition

ABSTRACT

A composition for shrinkable film which excels in heat-sealability, transparency, strength, and particularly low-temperature quick shrinking property and, therefore, suits production chiefly of packaging materials, a film made of the composition and a process for the manufacture of the film are disclosed. Specifically, the composition comprises one of the specific combinations of components (A), (B) and (C), i.e. the combinations of (A)+(B), (B)+(C) and (A)+(B)+(C), wherein (A) is non-rigid polyolefin resins such as ethylene vinyl acetate, (B) is an elastomer comprising a specific ethylene-α-olefin copolymer, and (C) is rigid polyolefin resins such as polypropylene. The packaging film excelling particularly in optical property, mechanical strength and low-temperature shrinking property is obtained by converting a homogeneous blend of the aforementioned composition, either in its crosslinked form or in its non-crosslinked form, into a tubular raw film, which is stretched at a temperature low enough for imparting a high orientation to the film. The process for the manufacture of this packaging film is also disclosed.

This is a division of application Ser. No. 949,253, filed Oct. 6, 1978,now U.S. Pat. No. 4,227,578.

BACKGROUND OF THE INVENTION

Packages formed with films are manufactured by a good number of methodswhich utilize to advantage the characteristics of the films such as thebag sealing method, twist wrapping method, thermal shrink wrappingmethod, cohesive wrapping method by use of specific films represented bySaran Wrap (product of Asahi-Dow Limited), strength wrapping method andthe like. These methods require respective wrapping characteristics. Foreach packaging method, therefore, it is important to select a film whosebasic material, composition, form and characteristic attributes bestsuit the wrapping characteristics of the particular method employed.

Of these packaging methods, this invention primarily aims to provide afilm particularly suitable for the shrink wrapping method. Neverthelessthe film of the present invention need not limit its uses but may be putto other uses satisfactorily. Thus, this is a unique multipurpose filmnever attained to date. For the convenience of illustration, therefore,the present invention will be hereinafter described with reference tothe film formulated to suit the shrink wrapping method.

Generally, the shrink wrapping method effects required wrapping byvirtue of the thermal shrinkability of a film stretched and oriented infixed directions, specifically resorting to a procedure of looselyprepackaging a given commodity with the film as by sealing, andthereafter thermally shrinking the film as enclosing the commoditytherein by means of a suitable heat medium such as the hot air, infraredray or hot water for thereby causing the film to shrink and come intoskintight contact with the overall irregular contour of the commodity.This method is characterized by providing a package which has abeautiful appearance, imparts an enhanced commercial value to thecontent, keeps the content in a hygienic condition and yet permits thecontent to be examined for its quality through visual observation or bysensation of touch. This method enables even a commodity of irregularshape or a plurality of commodities to be packaged with ample tightnessin a single piece and provides the content with effective protectionagainst vibrations and other impacts.

Further, the shrink wrapping method provides speedy packaging ascompared with the stretch wrapping method which is extensively used suchas in super markets. As an effective method for industrial packaging ofheavy articles of large dimensions which the stretch wrapping method isincapable of packaging, this shrink wrapping method is finding rapidlyincreasing acceptance and arresting keen attention.

Moreover, it permits packaging of commodities of shapes so irregular asto defy effective packaging by the stretching method and enables desiredpackaging to be accomplished without use of trays or other containers.It also enjoys greater tightness of package. In spite of all theseadvantages, the shrink wrapping method has a disadvantage that thepackage must be amply heated until the film shrinks to requiredtightness.

It is the oriented film or plasticized polyvinyl chloride (hereinafterreferred to as PVC) that is now used most widely for the shrinkwrapping. This is ascribable to the film's great merit of readilyundergoing thermal shrinkage of a high rate at relatively lowtemperatures and providing satisfactory shrink wrapping in a wide rangeof temperatures. On the other hand, this film nevertheless has adisadvantage that it provides heat sealability, preservability(liability of the plasticizer to degrade properties brought about by theorientation of film) and moistureproofness less than normally required,entails a hygienic hazard due to use of the plasticizer, emits noxiousgases such as chlorine-based gases when the film is cut by means ofheated wire, issues corrosive gases when the film, after use, is burntin an incinerator and, because of its inferior cold resistance, tends torigidify, embrittle and rupture when the packages using the film arestored at low temperatures or handled in cold districts.

In recent years, therefore, increasing attention has come to be focussedon a polypropylene type (hereinafter referred to as PP) film for use inthe shrink wrapping method. The PP film has a disadvantage that itprovides inferior shrinkability to the PVC film. The oriented film ofthe PP type is excellent in mechanical property, moistureproofness, heatseal strength, heat resistance and film modulus and, therefore, provesto be highly suitable for use as a film for the shrink wrapping.

Further, PP is advantageous over PVC in terms of raw material cost andbecause of low specific gravity. Because PP is a rigid, crystallinepolymer possessing a high softening point, the PP film requires heatingat a higher temperature for necessary shrinkage than the conventionaloriented films and exhibits a very slight degree of shrinkage at lowtemperatures in the neighborhood of 100° C. Thus, the PP film must beheated at high temperatures in the course of the shrink wrapping.Moreover since the allowable range of temperatures for the heating isnarrow and the dependency of the rate of shrinkage upon temperature isheavy, a locally uneven heating possibly given to the film at the timeof wrapping results in a notable uneven shrinkage which tends to causecreases, dots resembling pockmarks and other surface irregularitieswhich are undesirable from the viewpoint of practical use of film. Moreheating given to the film for the purpose of preventing such unevenshrinkage brings about a serious drawback that the content beingpackaged is excessively heated, the film is deprived of itstransparency, and the film is ruptured along the sealed portion andaround the air vents. Generally, the PP film is available preponderantlyin small thickness. If the thickness is increased, the PP film becomestoo rigid to permit successful shrink wrapping and tends to sustainrupture readily.

The conventional low-density polyethylene (hereinafter referred to asLDPE) film in its unalterated form does not permit sufficientorientation of molecules. The oriented LDPE film resulting from thetreatment of stretching, therefore, exhibits low thermal shrinkage andparticularly low thermal shrink tension, requires high temperature forshrinkage, offers poor film strength and optical property, produces lowbinding force in the package with respect to the article contained.Because of these inferior properties, the LDPE film which is produced inan increased thickness is put to special uses.

In the case of LDPE film, if the film is stretched thoroughly at a hightemperature exceeding its melting point by use of a high-energy ray soas to cause crosslinking of molecules, the oriented film enjoys highprocessibility, permits required orientation to be set effectively in arange of high temperatures, exhibits high thermal shrinkage and highthermal shrink tension and excels the LDPE film in various propertiessuch as optical properties including transparency and gloss, resistanceto heat and the like. In the range of high temperatures, however, thethermal shrinkage is not high enough to permit effective heat sealingand the film strength is degraded to impair the heat sealability andtear resistance.

Further, the oriented LDPE film has a disadvantage that the cutting andthe sealing of film by means of a heating wire are difficult to effect,the physical properties, particularly the optical properties aredegraded subsequently to the thermal shrinkage, the film strength islowered, and the film tends to sustain rupture and creases around airvents at the time of shrink wrapping. Because of these drawbacks, theshrink wrapping by use of the oriented LDPE film is inferior in terms ofspeediness of operation and finish.

As is clear from the foregoing description, one important requirementfor successful shrink wrapping resides in the fact that the film shouldpermit required packaging to be effectively carried out at lowtemperatures. This requirement is particularly significant when thepackaging is given to fresh food.

The oriented PP film is produced by a procedure of extruding the moltenpolymer through an annular die into a tubular raw film, suddenly coolingthe extruded tubular raw film, again heating the raw film at hightemperatures in the range of from 150° to 160° C. and simultaneouslyintroducing air into the interior of tubular raw film. The oriented LDPEfilm can be produced by the conventional procedure which is employed inbiaxially stretching. These processes are extremely difficult toaccomplish from the technical point of view because the films are highlyliable to sustain rupture.

Thus, the direct inflation method which involves a procedure ofextruding the molten polymer at a temperature in the range of from 180°to 220° C., for example, and thereafter suitably cooling the extrudedtubular film with ambient air and, at the same time, inflating the filmto a film of a desired size is generally employed.

The inflation method is characterized by being capable of producing adesired film readily and inexpensively. It nevertheless suffers from adisadvantage that the treatment entails irregular flow andcrystallization of molecules and impairs the optical properties of filmand the stretching fails to provide satisfactory setting of molecularorientation. Consequently, the thermal shrinkage and thermal shrinktension are deficient and high temperatures are required for ensuringtheir sufficiency. The film produced by this method, therefore, inimpracticable unless it is produced in an increased and put to specialuses. To overcome the disadvantage, there have been developed improvedmethods resorting invariably to a procedure of extruding LDPE in theform of a tubular film, exposing the film to a high-energy radiant rayunder suitable conditions for thereby inducing a partial crosslinkingreaction in the film and reheating and stretching the film so as toeffect required setting of molecular arrangement sufficiently withoutentailing random intermolecular flow. The conventional inflation method,however, produces a film which is not free from the aforementioneddrawbacks.

A good many methods have heretofore been suggested for producing filmsby mixing polymers of different olefins or mixing polyolefins with otherpolymers and subsequently inflating the resultant blends. For example,U.S. Pat. No. 3,682,767 discloses a method for producing a filmpossessing improved melt strength and heat sealability and exhibitingimproved make-and-fill property at the time of packaging a liquidcommodity by a procedure of mixing ethylene, an olefin type unsaturatedmonomer such as, for example, ethylene-vinyl acetate copolymer(hereinafter referred to as EVA) and a linear copolymer of ethylene withan α-olefin having a density in the range of from 0.93 to 0.96 g/cm³,such as, for example, a modified high-density polyethylene (hereinafterreferred to as HDPE) and subsequently extruding the resultant blend inthe form of a flat or tubular sheet. British Pat. No. 988,299 teaches aprocess for producing a printable polyethylene film by a procedure ofmixing EVA with LDPE or HDPE, causing crosslinking in the resultantblend either before or after molding, and subsequently stretching theblend in the form of film. And British Pat. No. 1,035,887 concerns aprocess for the production of a film excelling in low-temperatureproperties by a procedure of mixing LDPE with a linear medium-densitypolyethylene obtained by modifying ethylene with a small amount ofbutene and stretching the resultant blend.

As to manufacture of films, British Pat. No. 998,299 mentioned aboveinvolves a procedure of treating the aforementioned composition with aperoxide or a high-energy ray and thereby causing crosslinking andsubsequently stretching the crosslinked sheet at temperatures close toor slightly higher than the melting point of polyethylene and BritishPat. No. 992,897 adopts a procedure of treating EVA with a high-energyray and thereby causing crosslinking and subsequently stretching thecrosslinked sheet at elevated temperatures (preferably in the range offrom 100° to 120° C., for example). The films obtained of suchcompositions are devoid of the excellent optical properties, strengthproperties and low-temperature shrinking property enjoyed by theaforementioned PVC type films and they fail to exhibit satisfactoryfilm-forming property.

SUMMARY OF THE INVENTION

The invention carried out a study with a view to improving these filmsand their manufacturing methods and thereby eliminating their inherentdrawbacks. They have, consequently, developed a composition as the rawmaterials for the film which far excels in thermal shrinkage properties,particularly thermal shrinkage and thermal shrink tension at lowtemperatures and broadness of temperature range for thermal shrinkageupon temperature, optical properties, film sealing property and filmstrength and which, therefore, excels both plasticized PVC film and PPfilm and combines the characteristics of both the films, and a filmformed of said composition and a process for the manufacture of the filmwhich enjoys an outstanding workability.

BRIEF EXPLANATION OF DRAWINGS

FIG. 1 is a graph which shows the relation between the shrinkage of filmand the heat-treating temperature.

FIG. 2 is a graph which shows the relation between the shrink tension ofthe film and the heat-treating temperature.

FIG. 3 shows the result of the practical shrink-wrapping test of thevarious films, namely the range capable of obtaining the good wrappingfinish not having a wrinkling, a pockmark and a breakage when fourcucumbers were shrink-wrapped.

FIG. 4 shows the range capable of obtaining the suitable heat-sealingwhen the heat-sealing was carried out by the heating bar type sealer.

FIG. 5 shows the variation of the characteristic properties of the filmof Run No. 1. Example 1 in the stretch-working temperature, the area (A)is the area of the film of the present invention.

In the figure, curve 1 indicates the film of Run No. 2 Example 1. Curve2 indicates the film (17μ in thickness) of the commercial plasticizedPVC shrink film. Curve 3 indicates the commercial PP shrink film (16μ inthickness). Curve 4 indicates the commercial uncrosslinked low densitypolyethylene shrink film (50μ in thickness). Curve 5 indicates thecommercial crosslinked polyethylene shrink film (17μ in thickness).

DETAILED DESCRIPTION OF THE INVENTION

To be specific, the present invention relates to a composition whichcomprises one of the combinations of components (A), (B) and (C), namelythe combinations of (A)+(B), (B)+(C), and (A)+(B)+(C), wherein (A) is atleast one selected from the group consisting of LDPE and copolymers ofethylene with vinyl ester monomers, unsaturated aliphatic monocarboxylicacids and alkyl esters of said monocarboxylic acids which are allcopolymerizable with ethylene, (B) is an elastomer comprising a specificethylene-α-olefin copolymer, and (C) is at least one selected from thegroup consisting of crystalline PP, HDPE and crystalline polybutene-1(hereinafter referred to as PB-1), to a film manufactured by thoroughlymelting and blending said composition, extruding the resultanthomogeneous blend through an annular die, suddenly cooling the tubularsheet with a liquid refrigerant, causing the resultant solidified sheet,either immediately thereafter or subsequently to a treatment with ahigh-energy ray or incorporation of a peroxide aimed at inducingcrosslinking in the sheet during the subsequent application of heat, tobe heated to temperatures not exceeding 110° C., then cold stretchingthe heated sheet into a film at an area stretching ratio of from 5 to 30times the original dimension at a stretching temperature in the range offrom room temperature (20° C.) to 100° C., and further to a process forthe manufacture of said film. The film thus produced from thecomposition of this invention by the process also of this invention ischaracterized by possessing outstanding low-temperature shrinkability,film strength, optical properties and other characteristics which havenever been attained to date.

The polymer (A) to be used in the present invention is selected from thegroup consisting of LDPE and copolymers of ethylene with vinyl estermonomers, unsaturated aliphatic monocarboxylic acids and alkyl esters ofsaid monocarboxylic acids. LDPE possesses a density of not more than0.935 g/cm³, preferably not more than 0.925 g/cm³, and a melt index[determined in accordance with ASTM D-1238 (190° C.)] of from 0.2 to 10,preferably from 0.1 to 5. Examples of the copolymers satisfying therequirement include EVA, ethylene-acrylic acid copolymer,ethylene-methacrylic acid copolymer, ethylene-ethyl acrylate copolymer,ethylene-methyl methacrylate copolymer, and the like. In any of thesecopolymers, the amount of a monomer contained besides ethylene isdesired to be in the range of from 3 to 30% by weight, preferably from 3to 25% by weight. If the amount of the monomer is less than 3% byweight, the cold stretchability is somewhat inferior when the stretchingis carried out on the film in its uncrosslinked form. Besides, thefilm's strength, thermal shrinkability and sealing property are notsufficient. If the amount exceeds 30% by weight, the tubular sheet hasinferior processibility and the opposed surfaces of film undergo thephenomenon of mutual blocking to render the film handling difficult, andthe mixing property of the components to make up the composition, thestrength of film and the optical properties, etc. are impaired. Asdescribed above, the melt index of the polymer is in the range of from0.2 to 10, preferably from 0.3 to 5. If the melt index is less than 0.2,the mixing property of the components of the composition and theextrudability of the resulting blend are not satisfactory. If the meltindex exceeds 10, the blend fails to provide sufficient strength and theextruded sheet tends to sustain rupture readily at the time ofstretching. These drawbacks are suffered also when the sheet issubjected to the treatment for crosslinking.

Of the various possible copolymers usable as the component (A) in thecomposition of this invention, most desirable is ethylene-vinyl acetatecopolymer. In the case of a low-density polyethylene, the blend isdesired to be subjected to said treatment for crosslinking.

The thermoplastic elastomer comprising a copolymer of ethylene with atleast one α-olefin as the component (B) is a non-rigid copolymer ofethylene with at least one α-olefin selected from the group consistingof α-olefins having from 3 to 12 carbon atoms. As occasion demands, thiselastomer may be further copolymerized with a small amount of ahydrocarbon of the polyene structure such as, for example,1,4-hexadiene, ethylidene, norbornene, etc. Examples of the α-olefinsuitable for this purpose include propylene, butene-1, hexene-1,heptene-1, 4-methyl-1-pentene, octene-1, etc. Of these α-olefins,preferable are propylene and butene-1. In any of these copolymers, theethylene content is desired to fall in the range of from 20 to 90 mol%,more desirably from 40 to 90 mol%, preferably from 65 to 88 mol%.

These copolymers are of such nature that the density is not more than0.91 g/cm³, the Vicat softening point [as determined in accordance withASTM D-1525 (value under 1 kg of load)] is not more than 80° C.,preferably not more than 70° C. and the crystallinity in the rubberyzone generally ranges from substantial amorphousness to low partialcrystallinity of the order of not more than 30% of crystallinity degreedetermined with X-ray.

The component (B) is particularly desired to be a copolymer of ethylenewith propylene or butene-1, and this copolymer may, when necessary,incorporate therein a small amount of a compound of the diene structurein the form of a copolymer. It is, therefore, a thermoplastic elastomerin the form of a random copolymer obtained by the polymerization using acatalyst of the system produced with a vanadium compound and an organicaluminum compound. The elastomer possesses a melt index of from 0.1 to10, preferably from 0.2 to 6.

The polymer (C) is at least one selected from the group consisting ofcrystalline PP, HDPE and high molecular PB-1 which each possessrelatively high regidity and relatively high degree of crystallinity.The polymer has relatively high rigidity and desirably a Vicat softeningpoint of not less than 100° C.

The crystalline PP which is one of the members of the group from whichthe component (C) of the composition of this invention is selected is acrystalline PP with high isotacticity usually available on the market.It is desired to be a homopolymer of propylene or any of the copolymersof propylene with not more than 10 mol% of ethylene, 1-butene or someother α-olefin. It may be a mixture of these copolymers.

HDPE as one member of said group is a polyethylene produced by themedium- or low-pressure process and possessing a density of not lessthan 0.935 (g/cm³) which is usually available on the market. Thispolyethylene is desired to possess a melt index in the range of from 0.1to 10, preferably from 0.2 to 7. In the case of a copolymer, theethylene group content is desired to exceed 90 mol%, preferably to beabout 95 mol%. When the high-density polyethylene is used as thecomponent (C), the blend prepared for film is desired to undergo theaforementioned treatment for crosslinking. If the melt index is lessthan 0.1, the film made of the blend using such a component is impairedin the mixing property of components and optical properties. If the meltindex is more than 10, the blend fails to offer sufficient strength andthe sheet's stretchability is impaired. The polybutene-1 is desired tobe a crystalline homopolymer or copolymer of more than 90 mol% ofbutene-1 with other monomer. Unlike a liquid to waxy low molecularpolymer, these polymers are desired to possess a melt index in the rangeof from 0.2 to 10 for the same reason as mentioned above. Of the threepossible members of the aforementioned group, it is desirable to usechiefly the crystalline polypropylene. A mixture of polypropylene withhigh-density polyethylene may be used.

The composition of the present invention comprises one of the specificcombinations of components (A), (B) and (C), i.e. the combinations of(A)+(B), (B)+(C) and (A)+(B)+(C). The mixing ratio of these componentsis such as to satisfy:

0.05≦B/(A+B)≦0.90 in the first combination,

0.30≦B/(C+B)≦0.90 in the second combination, and

0.05≦B/(A+B)≦0.90 and 0.05≦C/(A+B)≦2.0 in the third combination,

and more desirably to satisfy:

0.07≦B/(A+B)≦0.70 in the first combination,

0.40≦B/(C+B)≦0.87 in the second combination, and

0.07≦B/(A+B)≦0.70 and 0.07≦C/(A+B)≦1.0 in the third combination,

and preferably to satisfy:

0.10≦B/(A+B)≦0.50 in the first combination,

0.50≦B/(B+C)≦0.85 in the second combination, and

0.10≦B/(A+B)≦0.50 and 0.10≦C/(A+B)≦1.0 in the third combination.

If the amount of the non-rigid component (B) is less than the allowablelower limit indicated above, the blend of any of the first, second andthird combinations fails to manifest the expected synergistic effectand, therefore, suffers from inferior processibility, lowered filmstrength and impaired optical properties and low-temperatureshrinkability. If the amount is more than the allowable upper limit, thetubular sheet produced from the blend is degraded in film-formingproperty and stretchability and becomes so soft as to entail thephenomenon of film-to-film blocking and the produced film exhibitsinsufficient heat resistance, sealability, strength and opticalproperties.

Of the three possible combinations of components, particularly desirableis the third combination, i.e. the combination of (A)+(B)+(C). To bemore specific, if the amount of the resin of the component (C) used inthe composition is smaller than 5 parts by weight, the blend exhibitsinsufficient stretchability and the extruded sheet tends to sustainpuncture and regain its original dimension and does not easily produce afilm of uniform thickness possessing the outstanding propertiesmentioned above and tends to give inferior finish to the package. Thefilm, when produced in a particularly small thickness, fails to providesufficient modulus. Consequently, the film has poor dimensionalstability and, therefore, tends to undergo deterioration by agingsimilarly to the plasticized PVC film, with the result that the heatresistance, heat seal strength, heat seal temperature range and finishof package are all adversely affected.

If the amount is greater than 200 parts by weight, the blend exhibitsinferior stretchability and tends to sustain puncture and the filmsuffers from insufficient optical properties, uniformly of wallthickness and low-temperature shrinkability. The mixed component (C)serves to improve not only modulus but also seal properties such as, forexample, thermal properties including heat resistance particularly inthe higher portion of the allowable temperature range.

As described above, this invention permits the quenched tubular sheetwhich has been produced from the composition obtained by using thespecific components in their respective specific amounts to be coldstretched with ample stability in the manner to be describedhereinafter. If the tubular sheet is further treated with a specifichigh-energy ray so as to have the gel content (insolubles in boilingxylene) or the melt index brought into a specific range, the componentsin the composition produce a synergistic effect such as to manifest thedesired cold stretchability (at temperatures in the range of from 20° to100° C.) under specific stretching conditions, giving rise to a film ofoutstanding properties.

Now, the composition produced by using the components in the preferredmixing ratio will be described. Generally, the crystalline PP [component(C)] is hardly crosslinked even when it is subjected to a treatment witha high-energy ray and it offers rather insufficient compatibility withEVA to be used as another component (A). In contrast, EVA when treatedwith a high-energy ray undergoes the reaction of crosslinking moreeasily than the ordinary low-density polyethylene. The elastomer of thecopolymer of α-olefin (B) exhibits rather high compatibility with bothpolypropylene and EVA and induces the reaction of crosslinking asreadily as EVA. Consequently, the synergistic effect brought about fromthe proper dispersion of the three components in the composition iscoupled with the synergistic effect which issues from the action of thehigh-energy ray. The combination of these synergistic effects isbelieved to result in the production of a film wherein there is formed aspecific, molecularly heterogeneous crosslinked matrix. The treatmentwith the high-energy ray, accordingly, improves notably the stable coldstretchability of the tubular sheet and the film's heat resistance andheat seal strength, enhances the thermal shrinkability and strength ofthe film at low temperatures, represses possible degradation in opticalproperties and physical properties after thermal shrinkage (such asoptical properties, seal strength and mechanical strength) and expandsthe range of packaging temperatures. Thus, the properties possessed bythe film which is produced from the crosslinked tubular sheet far excelthose possessed by the plasticized PVC film and PP film which haveheretofore been rated to be the best films.

The commercially available polyethylene film which has been thoroughlycrosslinked by the treatment with a high-energy ray possesses thedrawbacks mentioned above and, therefore, differs from the film of thisinvention. No matter whether the treatment for crosslinking is to beinvolved or not, the film made of the specific composition describedabove is required to possess a gel content of from 60 to 0% and a meltindex of not more than 10, preferably a gel content of from 50 to 0% anda melt index of not more than 5. Particularly in the case of the film tobe modified by the treatment with the high-energy ray, the insoluble gelcontent in boiling xylene is not more than 60% by weight and the meltindex is not more than 1.0. Desirably, the gel content is not more than50% by weight and the melt index is not more than 0.5. More desirably,the gel content is not more than 30% by weight and the melt index is notmore than 0.2. Preferably, the gel content is not more than 20 % byweight and the melt index is not more than 0.1. If the insoluble gelcontent is greater than the allowable upper limit mentioned above, theelongation of the stretched film is inferior and the heat sealabilityand the melt cutting and sealing of the film by the heating wire areinferior, the residual tension generated at the time of thermalshrinkage is high and the film tends to sustain rupture at the time ofpackaging. Further, the optical properties of the film are insufficient.If the melt index is greater than the allowable upper limit indicatedabove, the synergistic effects brought about by the treatment with thehigh-energy ray, namely the improvements in the processibility, thefilm's heat resistance, strength and heat sealability cannot beexpected. Thus, the gel content and the melt index are desired to fallwithin the respective ranges indicated above.

In the present invention, the composition of this invention may beeffectively used when it is mixed with some other composition insofar asthe amount of the additive composition does not impair thestretchability and various other properties of the film.

The film of the present invention is characterized by the opticalproperty [the value of Haze determined in accordance with ASTMD-1003-52] not exceeding 4.0%, more desirably 3.0% and preferably 2.0%.For example, the film of Run No. 2 of Example 1 is shown to possess ahighly satisfactory value of Haze of 0.8%. This value is particular tothe composition and the process of manufacture involved in thisparticular run of experiment. Because, the film can be processed withoutimpairing the properties acquired in consequence of the quenching of thecomposition in the tubular sheet. Moreover the tubular sheet can stablybe stretched in the form of bubbles at low temperatures below themelting point of the composition or preferably below the softening pointof the composition. And, the synergistic effects originating in thecomposition itself preclude otherwise possible occurrence of structuraldefects such as voids and permit the tubular sheet to be stretched inconjunction with mixed components distributed in fine particles, givingrise to a film of flat surfaces involving no appreciable scattering oflight. This possibly explains why the film has particularly hightransparency.

The low-temperature shrinkability is one of the important propertieswhich a given film is required to possess when the film is used for thepurpose of shrink wrapping. When the film is tested for its thermalshrinkage at varying temperatures, the low-temperature shrinkability isexpressed by the value of the temperature which is required for thepurpose of obtaining a specific shrinkage of 20% or 40% (to be expressedby an average shrinkage in the longitudinal and lateral directions). Thelower the value of this temperature, the better the low-temperatureshrinkability. Generally, the shrinkage which the film to be used forshrink wrapping is required to possess is not less than 20%, preferablynot less than 40%. To be specific, the thermal shrinkage is obtained bya procedure of preparing a square test piece cut from a given film,inscribing a longitudinal and a lateral mark each of a specifieddimension on the test piece, sprinkling the test piece with a powdersuch as of talc so as to repress its surface tackiness which oftenimpedes convenience of handling, treating it with hot air of aprescribed temperature for five minutes for thereby causing the testpiece to shrink, finding changes in the longitudinal and lateraldimensions of the marks and the found changes. The thermal shrinkage isexpressed by the average of the longitudinal and lateral shrinkage. Thisthermal shrinkage is found at a varying temperature. The temperatures atwhich the film gives 20% and 40% of thermal shrinkage are reported astemperatures for shrinkages of 20% and 40% respectively.

In the case of the film of this invention to be used for shrinkwrapping, the value of this temperature is small. As shown in FIG. 1 tobe described afterward, the commercially available polypropylene filmfor shrink wrapping has 120° C. as the temperature of 20% of shrinkageand 134° C. as that of 40% of shrinkage as indicated by the curve 3,whereas the film of this invention has 53° C. as the temperature for 20%of shrinkage and 72° C. as that of 40% of shrinkage as indicated by thecurve 1. The magnitude of low-temperature shrinkability in thisinvention is expressed by the temperature of 20% of shrinkage. It isdesired to be not more than 85° C., desirably not more than 75° C. andpreferably not more than 70° C. Although this value is affectedsecondarily by the stretching temperature and the composition, the factthat this value is on a low level constitutes one of the characteristicsof the cold orientation of the present invention. If this value islarge, required thermal shrinkage is not effected unless the film isexposed at a fairly high temperature for a long time at the time of itsactual use. Consequently, the magnitude of heat generated by the heatermust be increased and the speed of the packaging operation is lowered.Further, there is a possibility of the heat being transferred to thecommodity being packaged. Such transfer of heat proves undesirable wherethe commodity being packaged is highly vulnerable to heat, degradable ordeformable by the action of heat such as fiber or fresh food. In thecase of a film whose curve of shrinkage rises sharply at hightemperatures, the film's shrinkage is heavily varied even by a veryslight change near the shrinkage temperature at the time of packaging.When the film is loosely wrapped around a commodity and the loosepackage is passed through a shrinkage tunnel, a slight shortage in theoverall temperature of the hot air blown against the film results ininsufficient shrinkage, so that the film fails to come into skintightcontact with the contour of the commodity. If the temperature isslightly higher, the film is fused and sustains rupture or it isdeprived of transparency and optical homogeneity.

If the value of this temperature is extreme, the film wound up in a rollundergo a dimensional change even at normal room temperature. Thecommercially available PVC plasticized film to be used for shrinkwrapping has 58° C. for 20% of shrinkage and 88° C. for 40% of shrinkageas indicated by the curve 2 in the graph of FIG. 1. This suggests thatthis film possesses desirable low-temperature shrinkability, theshrinkage property varied smoothly with the temperature.

To date, no other commercially available film than the plasticized PVCfilm has had such desirable shrinkage property and strength.

The film of this invention has attained such excellent properties and,in this respect, defies all comparisons. The thermal shrink tensionexhibited at the time of shrinkage constitutes one of the importantthermal shrinkage properties, comparable with the thermal shrinkagewhich is an important factor when the film is used for the purpose ofshrink wrapping. Even if the thermal shrinkage is high, the film failsto fit tightly to the commodity being packaged during or after the stepof packaging when the tension generated in the film at the time ofshrinkage is low or deviates in the direction of higher temperatures aswill be described afterward. The film, then, fails to produce desiredbinding force and can no longer serve for the purpose of shrinkwrapping.

If the value of this tension is insufficient even to the slightestextent for the purpose of producing binding force, the film is requiredto have its thickness increased to make up for the insufficiency. Suchincrease in the film thickness is uneconomical and inconvenient.Generally, this maximum value desired to be not less than 50 g/mm²,preferably not less than 80 g/mm². As shown in FIG. 2, the commerciallyavailable polyethylene film for shrink wrapping has a thermal shrinktension of not more than 10 g/mm², about 5 g/mm² as indicated by thecurve 4. Thus, the film is applicable to limited uses. The film of thisinvention has a value of 230 g/mm² as indicated by the curve 1 in thesame graph. Generally, the film of this invention has a sufficientlyhigh value in the range of from 100 to 400 g/mm².

In the case of the low-temperature shrinkable film, this shrink tensionis not sufficient unless it is manifested at a temperature close to thetemperature corresponding to the shrinkage. The temperature-dependencycurve of the shrink tension must be well balanced with theshrinkage-temperature curve (expressed by the average of the values forlongitudinal and lateral directions). At times, the thermal shrinktension is desired to occur in an increased range of temperatures. Inthis respect, the film of the present invention can be adjusted byproperly selecting the composition and treatment.

In the present invention, the stiffness of the film can freely beadjusted in the range of from fair softness to considerable ridigity byvarying the composition within the specified range.

The film of the present invention is further characterized by possessinga particularly high tensile strength. The strength at rupture is atleast 5 kg/mm² (as determined in accordance with the method of ASTMD-882-67), preferably not less than 7 kg/mm². The elongation at ruptureis desired to be not less than 50%, preferably not less than 100%, andmore preferably not less than 150%. The dart impact strength isdetermined by following the method of ASTM D-1709-67 with necessarymodifications. It is expressed by the value which is obtained by using aspecial dart whose missile head is provided with a grooved edge tofacilitate rupture of the film. The film of this invention is alsocharacterized by the fact that the dart impact strength has aparticularly high value. For example, while the PVC film and the PP filmhave 18 and 12 kg·cm, the film in the Run No. 16 has a value of 48Kg·cm, the value comparable with that obtained by heavy bags of LDPE of100 to 150μ in thickness available on the market. The dart impactstrength is generally not less than 15 kg·cm, preferably not less than20 kg·cm, and more preferably not less than 25 kg·cm (as expressed onthe basis of 17μ).

The fact that the tensile strength is high and the elongation is greatas described above means that the film is tough and highly resistant totear. Thus, the film proves highly advantageous for the protection ofpackages and permits a reduction in the film thickness.

The film of this invention possesses a strength at rupture of 14.5kg/mm² and an elongation of 185% as shown afterward in Run No. 2.Generally, when the strength is enhanced by orientation, the film tendsto lose its elongation to an extreme extent. In the case of thecommercial film which is thoroughly crosslinked (with the insoluble gelcontent in boiling xylene brought to 67% by weight) and consequentlyoriented sufficiently as described hereinafter, the strength is 6.9kg/mm² and the elongation is 45%, indicating that the film is highlyliable to rupture. The film of this invention is not limited to use inshrink wrapping. By virtue of its excellent toughness, it can beutilized widely as an industrial film.

By the after-treatment resorting to heat setting, the temperature forthermal shrinkage and the orientation balance in the longitudinal andlateral directions can freely be adjusted so as to adapt the film ofthis invention for other uses or enable the film to be laminated withvarious other films.

Now, a typical process for manufacturing a film for shrink wrapping fromthe composition of this invention will be described in detail hereinbelow.

This is a process for manufacturing a high-strength oriented filmexcelling in optical properties and low-temperature shrinkage propertiesand having a wide range of effective packaging temperatures, whichprocess comprises thoroughly mixing and melting one of theaforementioned combinations of components, i.e. the combinations of(A)+(B), (B)+(C), and (A)+(B)+(C), extruding the resultant homogeneousblend through an annular die, suddenly solidifying the extruded tubularraw film with a liquid refrigerant for thereby producing a tubular rawfilm sufficiently free from partiality in thickness, causing the tubularsheet, either immediately stretching thereafter or subsequently to atreatment conducted by irradiation of a high-energy ionizing radiant raywith a view to modifying the composition of the tubular raw film so thatit acquires an insoluble gel content of not more than about 60% inboiling xylene and a melt index of not more than 1.0, to be heated to atemperature in the range of from normal room temperature to 110° C., andintroducing air into the interior of the tubular raw film at astretching temperature in the range of from 20° C. (room temperature) to100° C. for thereby effecting cold orientation at an area stretchingratio of from 5 to 30 times the original dimension.

Now, the process of the present invention will be described withreference to the most desirable combination of components. Thecomponents of the combination are melted under heat and thoroughlyblended. The resultant blend is extruded at an extruding temperature inthe range of from 180° C. to 280° C. through a shape die adaptedeffectively to avoid giving to the extruded sheet uneven wall thicknessand imparting thereto heat and time hysteresis, and the extruded tubularraw film is suddenly cooled on the outer periphery thereof uniformlywith a liquid refrigerant to produce a tubular raw film of amplehomogeneity (in terms of both external shape and internal structure).This tubular sheet is immediately subjected in its unaltered form to thesubsequent heat treatment followed by the step of stretching.Alternatively, it is irradiated with a high-energy ionizing radiant rayof 2 to 15 Mrads such as, for example, an electron ray, β-ray or γ-rayradiated from a radio-isotope or it is radiated with an ultraviolet rayin the presence of a sensitizer (such as, for example, benzophenone orperoxide) incorporated in advance in the composition for the purpose ofmodification such that the resultant tubular sheet exhibits an insolublegel content of not more than about 60% by weight in boiling xylene and amelt index of not more than 1.0. The reason for these particular rangeshas already been described. Any deviation from the specified range ofenergy of the irradiation is undesirable: If the irradiation exceeds 15Mrads, there ensue undesirable phenomena such as severance of moleculesdue to decomposition (embrittlement of resin) and coloration andodorization of the resin. If the irradiation falls short of 2 Mrads, thedesired effect of irradiation cannot be obtained. From the viewpoint ofphysical properties and ease of processibility, preferable irradiationis obtained in the range of from 2.5 to 10 Mrads. This modification mayotherwise be obtained by a thermal crosslinking method using a peroxide.The tubular raw film thus treated is then heated to a temperature in therange of from normal room temperature to 110° C., preferably not morethan 90° C., and more preferably not more than 80° C., i.e. thetemperature at which the main crystalline component used in thecomposition remains undissolved and, at the same time, inflated in theform of a bubble with an ample inner pressure in the range of from 100to 1000 mm H₂ O of water column at a temperature in the range of fromroom temperature (20° C.) to 100° C., preferably from 30° C. to 90° C.,and more preferably from 30° C. to 80° C., i.e. the temperature which islower than the melting point of the main crystalline component used inthe mixed composition, preferably lower than the Vicat softening pointof the mixed composition. In this manner, the film of the presentinvention is obtained advantageously. The optimum area stretching ratio,though variable to some extent with the prevailing temperature at thetime of stretching, is desired to fall in the range of from 5 to 30times the original dimension, preferably from 7 to 30 times the originaldemension, and more preferably from 10 to 20 times the originaldimension. The lateral stretching ratio is generally desired to fall inthe range of from 2 to 7 times the original dimension, preferably from 3to 6 times the original dimension. For the cold orientation to beobtained effectively without entailing the possibility of film puncture,it is imperative that the composition should fall within the rangespecified herein and it is equally important that the tubular sheetshould enjoy ample uniformity. If the wall thickness of the tubular rawfilm involves a deviation of 20% or more, there is a fair possiblity ofthe raw film sustaining puncture in the course of stretching, makingeffective stretching impracticable. The allowable deviation of wallthickness of the tubular raw film is within ±5%, preferably within ±3%.Stable stretching of the tubular raw film into a film is advantageouslyaccomplished by first fixing the longitudinal stretching ratio throughadjustment of the ratio of rotating speeds of the feed nip rolls and thetakeup nip rolls and thereafter adjusting the introduction of air intothe tubular raw film now inflated in the form of a bubble so as toeffect the stretching up to the end point of bubble inflation(immediately before the point of blushing) and bring the lateralstretching to termination. Because of the relation between the innerpressure applied to bear on the bubble and the diameter of the bubble,the tubular raw film is desired to have as large a diameter as possible,generally greater than 50 mm, preferably greater than 100 mm. In dueconsideration of the physical properties of the film to be produced, thestretching temperature is desired to be the lowest level at which thestability of the bubble is retained. For practical purpose, it sufficesto determine the degree of stretching on the basis of the compositionbeing used, with due consideration paid to the balance with the bubblestability (enough to preclude possible film puncture). Since thetransfer of heat to the film is small, a fact which characterizes theprocess of the present invention, the thickness of the film can befreely selected from a wide range from a very small order of 5 to 6μ toa very large order of 100 to 150μ. This general choise of the filmthickness afforded by the present invention has never been attained withthe conventional films.

The film which is obtained by the process of this invention possessesthe outstanding properties mentioned above and, more often than not, hasa highly limited deviation of film thickness of the order of ±5% afterthe step of stretching. A possible reason for this advantage is that thehigh inner pressure applied to bear upon the bubble imparts a strongstretching force to the film and the heat hysteresis generally involvedin the course of heating and cooling is notably small and, consequently,the film enjoys high uniformity and stability. The optical properties(both Haze and gloss) of the tubular raw film appear to be quiteinferior. They are notably improved, however, after the tubular raw filmhas undergone the treatment for cold orientation by the process of thisinvention. A possible reason for this improvement of optical propertiesmay be that the resin particles distributed in the form of islandsthroughout the sheet are changed in change in consequence of the coldorientation. Since the process of this invention enables the distributedresin particles to be oriented and flattened out, the film no longercauses random scattering of light. It is, accordingly, inferred that thestretching of the film is advantageously attained even at lowtemperatures to produce a strong film, notwithstanding the compositionis a blend not mixed so thoroughly as to induce dispersion of molecules.

In the present invention, the components which make up the compositionmanifest synergistic effects respectively. When any of the componentsused in the composition is relied upon to impart added strength to thefilm, it will neither bring about a drawback often experienced in asimilar situation nor cause any degradation of strength. This advantageis never attained by the ordinary stretching method which requires thesheet to be heated up to or over its melting point. In the case of theconventional film, the stretching temperature must be elevated to havethe optical properties of the film improved. Use of the elevatedstretching temperature renders the desired orientation all the moredifficult and tends to degrade the film strength.

The same thing also applies to the use of a stretching temperature whichis close to the melting point. At such a stretching temperature, theoptical properties of the film obtained are far from being satisfactoryand the mixed composition happens to reach the point where the tubularsheet becomes intolerably brittle. Thus, the film sustains puncture andfails to acquire advantageous properties. As illustrated in thepreferred embodiments of this invention afterward, the cold orientationaimed at by the present invention can be effectively attained at a verylow temperature such as, for example, 32° C. This is an unprecedentedachievement, which is not materialized unless the specific composition,the specific treatment with a high-energy ray which is optionallycarried out, the uniform quenching of the tubular raw film and thespecific conditions of stretching are combined to produce synergisticeffects. It goes without saying that the film sustains puncture andcannot be effectively stretched when the quenching given to the tubularraw film lacks uniformity and the film of the present invention cannever be obtained when the stretching temperature actually used deviatesfrom the specific range described above. When the stretching of thetubular raw film is carried out simply by the tenter method, the filmobtained readily sustains rupture and fails to exhibit the outstandingproperties peculiar to the film of this invention. It is ideal to havethe tubular film stretched monoaxially or biaxially, more preferablybiaxially in a tubular form under the stretching conditions mentionedabove.

The characteristic processibility of the film and the characteristicattributes of the film obtained by the present invention are believed tobe ascribable to the fact that the components making up the compositionpossess suitably balanced compatibility, the fact that the components onwhich the individual properties such as crystallinity, softening pointand modulus of elasticity all function independently and the componentson which such properties function in good harmony cooperatesynergistically to bring about ideal effects and the fact that theeffect of the treatment with a high-energy ray also participates in thesynergistic function mentioned above.

As described in one of the comparative examples afterward, when anattempt was made to stretch a tubular raw film obtained from EVA, thebubble of the raw film punctured before it was sufficiently inflated,making it impossible to continue the biaxial stretching of the raw filmat the low temperatures specified herein. U.S. Pat. No. 3,244,680 citesan example wherein a high-molecular EVA copolymer was compression moldedinto a circular disc and subjecting the circular disc to batchstretching by use of a multiaxial chuck (radial stretcher) attemperatures in the range of from 30° to 60° C. The film obtained bythis method can never be obtained by the process of this invention.Thus, this invention differs from the process of said U.S. patent interms of composition, process and film.

The mixed composition of this invention can be converted effectivelyinto a film by a procedure of closing the free end of the tubular rawfilm batchwise and stretching the tubular raw film by hand whileintroducing air into the interior thereof through the other end forthereby allowing the tubular raw film to form a cold-oriented bubblestably in the ambient air maintained at temperatures in the range offrom 20° to 40° C. None of the components, when used singly, can form abubble and can be stretched biaxially even in a continuous operation bythe process of this invention.

FIG. 5 represents the processibility data obtained in Run No. 1 andexpressed in terms of characteristic elements. The zone (A) contains thedata obtained of the stable processing according to the presentinvention and the zone (B) those of unstable processing. In the latterzone, the optical properties, strength and film thickness at the time ofstretching are heavily degraded. In the zone (C), the molecular flow inthe film is so heavy as to impede effective setting of orientation, sothat the film strength is lower and the elongation is greater. Thistrend substantially exists when the tubular raw film is given atreatment for crosslinking. The crosslinking treatment serves toalleviate the decline of strength in the zones (B) and (C) and tends toenhance only slightly the strength in the zone (A). The trend withrespect to the optical property (Haze) and the low-temperatureshrinkability remain unaffected by the crosslinking treatment.

The composition and the process of this invention may be appliedeffectively to the manufacture of a film by monoaxial stretching. Inthis case, the properties of the film are attained in the direction ofthe stretching. Further, the tubular raw film which is obtained byextruding the homogeneous blend of the composition and subsequentlyquenching the extruded raw film can be used as a film of high strengthat rupture and as a composition with improved heat sealability andelastic modulus and good seal strength, because it has been modified soas to be readily cold oriented at normal temperatures and good forstability at inflation. For example, it may be used as a film forgeneral wrapping or as a low-oriented film for stretch wrapping, bagfilm, etc.

Besides, the composition, treatments and stretching method involved inthe present invention can be applied in any freely chosen combination tothe component layers of a multi-layered film taken singly or incombination.

Now, the composition and film of this invention, and the process for themanufacture of this film will be described more specifically hereinafterwith reference to preferred embodiments, which are solely illustrativeof and never limitative of this invention.

EXAMPLE 1

To 100 weight parts of the composition composed of 82% by weight of EVA(a₁) (the vinylacetate unit content 10% by weight, the melt index 1.0)and 18% by weight of the ethylene-α-olefin copolymer (b₁) (α-olefin ispropylene, said copolymer comprises 15 mol% of propylene and 4% byweight of ethylidine norbornene) having the melt index of 0.45, theVicat softening point of not more than 40° C. and the density of 0.88g/cm³, were mixed 18 weight part of the crystalline PP (c₁) having themelt index of 1.0, the density of 0.88 g/cm³ and the Vicat softeningpoint of 146° C., and the plasticized kneading composition was extrudedat the maximum temperature of the cylinder part of 250° C. from theannular die 150 mm in diameter having the slit of 1.5 mm provided withthe mixing head type screw 65 mm in diameter and the ratio (L/D) of 37.Then the extruded product was quenched at the position which was about10 cm distance from the lip of the die by water which was uniformlyflowed out from the ring. Thus, there was obtained the raw tubular film100 mm in diameter, 200μ in thickness, partiality of ±1.8% in thickness.The said composition had the Vicat softening point of 75° C. Theobtained raw tubular film was treated with the electron ray of 500 KVenergy in the dose of 5 Mrad at the normal temperature so as to be thegel % of 3% by weight in the boiling xylene and the melt index of 0.07(Run No.2), while the said composition was directly proceeded to thefollowing stretching step without radiating the heigh energy ray (RunNo.1).

The raw tubular film was passed between the two pairs of the deliverynip rolls and the draw nip rolls respectively, while passing said rolls,the raw tubular film was heated to the temperature of 36° C. by the hotair and then was continuously inflated under the inner pressure of thewater head of 400 mm by blowing air within the tubular film andstretched by 3.5 times in the longitudinal direction and 3.3 times ofthe transverse direction, the cold air of 20° C. was blown to the filmfrom the air ring apparatus at the end of the stretching step to coolthe film. The film was fold up by the deflator and then taken up by thenip rolls and separated to the two sheets of film by slitting the edgesof the film in the longitudinal direction. Each of which was winded upunder the certain tension whereby the films 17μ in thickness (Run No.1and No.2) were obtained. Table 2 showed the characteristic properties ofthe resulting film in comparison with those of the commercial threesorts of films.

The stretched film obtained (for example Run No.2) had good opticalcharacter of Haze of 0.8% and the superior strengths of the tensilestrength of 14.5 kg/cm², the elongation of 185% and the dart impactstrength of 37 kg·cm in comparison with that of 20 kg·cm in thecommercial plasticized PVC shrink film (17μ in thickness), 12 kg·cm inthe PP shrink film (16μ in thickness). The high dart impact strength wasone of the characteristics of the film of the present invention. Asshown in Table 1 and FIG. 1, the film had the following low temperatureshrinking properties; 53° C. at 20% shrinkage, 72° C. at 40% shrinkage.The curve in FIG. 1 showing the interrelation between the heat-treatingtemperature (°C.) and the shrinkage (%) displayed the gentle slopingpattern similar to the commercial PVC shrink film. Furthermore, thisfilm had good shrinkage character toward the low temperature side.

This film had the maximum shrink tension of 230 g/mm² which was a highlevel. In the practical test of wrapping four cucumbers, wrapping wascarried out by passing the wrapped film for 3 seconds through theconventional tunnel over which was blown out the hot air of 90° C.thereby obtaining the good wrapping finish tightly fitted with goods andnot having any wrinkling and not depressing good optical character aftershrinkage. As shown in the oblique portion of FIG. 3, No.1, the varioustests were carried out by changing the hot air temperature when theshrinking wrapping was carried out and the staying time within thetunnel. From the test result, it was found to be able to smoothly carryout good wrapping at the broader range of the heating temperature withthe broader speed range from the low temperature side.

While the commercial shrink film of polypropylene did not almost shrinkat 90° C. and remained the wrinkle on the sample, the satisfactoryshrinking could not be accomplished without the high shrinkingtemperature of 170° C. Even if the heating temperature was furtherraised and the staying time was lengthened, the wrapping film was brokendue to pitting and became opaque. The optimum shrink temperature rangeof the film was very narrow. The commercial shrink film of PVC had lackof the shrinkage and remained the wrinkle under the same wrappingcondition as mentioned above. Therefore, the shrinking temperature of150° C. was demanded.

The shrink film of the commercial crosslinked polyethylene was notsuitable to the wrapping film since it could not shrink without the hightemperature of 170° C., the film was easy to break at the sealed partand moreover, was apt to occur much breakage, the good wrapping range ofthe film was judged from the shrinkage, the binding force, the hole atthe sealing part, the rupture from the air vent part and thedevitrification phenomenon of the film after wrapping. Furthermore,judging from the good wrapping finish, the film Run No.2 of the presentinvention was the best one. Similar results were obtained in the filmRun No.1 of the present invention.

Hereafter, the strength, the elongation and the heat-shrinking propertyof the film were shown by the mean value between those of thelongitudinal and transverse directions since said characters of the filmhad in the longitudinal and transverse directions in good balance.

                                      TABLE 1                                     __________________________________________________________________________    Shrinking                                                                     temp. (°C.)                                                                   50  60  80  100 120 140 160 180 200                                    __________________________________________________________________________    Heat shrink-                                                                  age (%)                                                                              16/17                                                                             26/27                                                                             49/47                                                                             65/63                                                                             71/70                                                                             74/74                                                                             76/77                                                                             77/78                                                                             83/80                                  Run No.1/                                                                     Run No.2                                                                      __________________________________________________________________________

                                      TABLE 2                                     __________________________________________________________________________                               Comparative                                                           Run No. sample                                             Property      Unit 1   2   I   II  III                                        __________________________________________________________________________    Hage          %    1.0 0.8 1.7 2.8 2.5                                        Gloss (20°)                                                                          --   142 150 123 105 103                                             20% shrinkage                                                                          °C.                                                                         53  53  58  120 100                                             temperature                                                              Thermal                                                                            Maximum  %    83  80  58  72  76                                         Property                                                                           shrinkage                                                                     Maximum shrink                                                                         g/mm.sup.2                                                                         180 230 108 208 192                                             tension                                                                       Temperature                                                                            °C.                                                                         70  69  115 115 102                                             at peak                                                                  Tensile strength                                                                            kg/mm.sup.2                                                                        12.0                                                                              14.5                                                                              8.0 14.4                                                                              6.9                                        at break                                                                      Elongation at break                                                                         %    200 185 145 125 45                                         Dart impact strength                                                                        kg . cm                                                                            32  37  20  12  8.5                                        __________________________________________________________________________     Note:                                                                         Gloss was measured in accordance with ASTMD 2454  65T.                        I is commercial PVC shrink film.                                              II is commercial PP shrink film.                                              III is commercial crosslinked polyethylene shrink film.                  

The film of the present invention was remarkably good in the range andstrength of heat-sealing in comparison with another comparative Run Nos.1, 2 and 3 when said film was heat-sealed by the heating bar typeheat-sealing machine.

The extent capable of heat-sealing was that surrounded by the obliquelines of No.1, FIG. 4. The axis of abscissa showed the temperature ofthe heat-sealing bar. The lower limit of the temperature was thatcorresponding to 50% probability between the case of immediately peelingoff the film without being sealed and the case of causing breakage ofthe film from the sealed part when the sealed film was pulled. The upperlimit of the temperature was that capable of cutting off the film bymelting when the film was pressed with the heating bar. Press wascarried out under the pressure of 1.3 kg/cm². The sealing strength underthe optimum condition was 1.3 and 1.5 kg/15 mm width in Run No.1, 2respectively, while said strength was 0.6, 1.1 and 0.7 kg/15 mm width inanother comparative examples a, b and c respectively. The film of thepresent invention had large strength and broad sealing range.

EXAMPLE 2

EVA (a₂) (the vinyl acetate group content; 15% by weight, the meltindex; 0.7) and ethylene-α-olefin copolymer elastomer (b₂) (α-olefin ispropylene, and 20 mol% of α-olefin group are contained, the melt index:0.25, the density: 0.88 g/cm³, and the Vicat softening point: less than40° C.) and the crystalline PP (C₂) (ethylene group content; 5% byweight, the melt index: 0.6, the Vicat softening point: 120° C., thedensity: 0.87 g/cm³) were mixed in the ratio as mentioned in Table 3 andextruded according to the process of Example 1 to obtain the raw tubularfilm (150μ in thickness and partiality of ±1.8% in thickness). Then theobtained film was extruded without any cross-linking treatment at thestretching temperatures of 41°, 51°, 53°, 60°, 75° and 79° C. in RunNos. 3-8 respectively thereby being manufactured the stretched filmshaving good stability and 14μ in thickness.

Each of the stretched film had less partiality of ±6-8% in thickness thegood stretching workability and dart impact strength of more than 25Kg.cm.

The physical properties of each film were shown in Table 4.

                  TABLE 3                                                         ______________________________________                                                 Run No.                                                              Composition                                                                              3       4      5    6    7      8                                  ______________________________________                                        a.sub.2    90      70     50   80   60     40                                 b.sub.2    10      30     50   20   40     60                                 c.sub.2    10      30     30   70   100    70                                 Vicat softening                                                               point of the                                                                  mixed composi-                                                                           64      68     62   88   93     84                                 tion (°C.)                                                             ______________________________________                                    

                                      TABLE 4                                     __________________________________________________________________________                       Run No.                                                    Property      Unit 3   4   5   6   7   8                                      __________________________________________________________________________    Hage          %    0.8 1.0 1.1 1.2 1.3 1.3                                         20% shrinkage                                                                          °C.                                                                         55  57  59  63  68  60                                          temperature                                                                   40% shrinkage                                                                 temperature                                                                            °C.                                                                         75  78  75  80  82  79                                     Thermal                                                                            Maximum                                                                  property                                                                           shrinkage                                                                              %    80  78  75  74  72  73                                          Maximum shrink                                                                tension  g/mm.sup.2                                                                         220 180 280 175 160 150                                         Temperature                                                                   at peak  °C.                                                                         60  68  72  71  80  75                                     Breakage strength                                                                           Kg/mm.sup.2                                                                        11.5                                                                              13.7                                                                              15.0                                                                              14.0                                                                              12.9                                                                              11.6                                   Elongation at                                                                 break         %    180 190 250 220 160 170                                    __________________________________________________________________________

As mentioned above, the practical wrapping test of the resulted film wascarried out according to the wrapping operation of Example 1. The filmhad good wrapping finish without occuring any wrinkling on the finishingsurface. The film was suitable to various uses with good result in thewrapping. The wrapping test was carried out using the shrink films ofRun No.4, the commercial PP and PVC respectively. The test was carriedout by wrapping with the film to be test a king crab which is therepresentative angulated goods. The test results were as follows: The PPand PVC films caused the breakage by spines of the king crab, while thefilm of Run No.4 gave good wrapping finish. The PP and PVC films becamebrittle during the storage and was apt to cause the breakage since thePP and PVC films were inferior to the low temperature resistance, whilethe film of No. 4 was no problems in wrapping ability.

EXAMPLE 3

EVA (a₃) (the melt index: 0.7, the vinylacetate group content: 13 weight%), ethylene-α-olefin copolymer elastomer (b₃) (the melt index: 0.25,the Vicat softening point: less than 50° C., the density: 0.88 g/cm³,α-olefin is butene-1 and α-olefin group content: 20 mol %) and thecrystalline PP (C₂) (mentioned above) were extruded and stably stretchedin the mixing ratio and the conditions as shown in Table 5 according tothe process of Example 1 under the stretching temperatures of 32°, 35°,40°, 51°, 53° and 50° C. which were the temperatures less than the Vicatsoftening point of the mixed composition in Run Nos. 9-14 respectivelywhereby the stretched films having 18μ in thickness were obtained.

Each of the film had less partiality of ±6-8% in thickness.

The physical properties of the resulted films were shown in Table 6.

                  TABLE 5                                                         ______________________________________                                               Run No.                                                                Composition                                                                            9       10      11    12    13     14                                ______________________________________                                        a.sub.3  90      70      50    80    60     40                                b.sub.3  10      30      50    20    40     60                                c.sub.2  10      30      30    70    100    70                                Dose (Mrad)                                                                            3       5       10    7.5   7.5    5                                 Gel (%)  1.5     2.5     20    12    8      1.0                               MI       0.1     0.07    less  0.08  0.09   0.15                                                       than                                                                          0.05                                                 ______________________________________                                         Note: Unit is based on the weight part.                                  

                                      TABLE 6                                     __________________________________________________________________________                  Run No.                                                         Property      Unit 9   10  11  12  14  14                                     __________________________________________________________________________    Haze          %    0.6 0.6 1.0 1.2 1.5 1.1                                    Gloss (20°)                                                                          --   157 155 153 147 138 150                                         20% shrinkage                                                                          °C.                                                                         50  51  52  53  57  54                                          temperature                                                              Thermal                                                                            Maximum  %    77  76  77  78  82  79                                     property                                                                           shrinkage                                                                     Maximum shrink                                                                tension  g/mm.sup.2                                                                         240 230 220 215 200 205                                         Temperature                                                                            °C.                                                                         60  64  65  72  75  70                                          at peak                                                                  Tensile strength                                                                            Kg/mm.sup.2                                                                        12.8                                                                              13.9                                                                              15.9                                                                              16.0                                                                              13.5                                                                              13.5                                   at break                                                                      Elongation at %    250 230 210 255 195 220                                    break                                                                         Dart impact   Kg . cm                                                                            38  35  32  40  32  30                                     strength                                                                      __________________________________________________________________________

As mentioned above, the practical wrapping test was carried out usingthe said films according to the wrapping operation of Example 1. Thegood wrapping finish without causing any wrinking on the finishingsurface was obtained in all tests.

EXAMPLE 4

The raw tubular films 200μ in thickness and partiality of ±2.0% inthickness were manufactured using the polymer composition, the ratio asshown in Table 7 according to the process of Example 1. The resulted rawtubular films were stretched under the stretching temperatures of 42°,51°, 48°, 66°, 49°, 35° and 70° C. which was less than the Vicatsoftening point of each film of Run Nos. 15-21, and stably stretchedrespectively thereby obtaining the films having 17μ in thickness.

The characteristic properties of this films showed in Table 8.

In order to test the bubble stretching stability by batch method, testpieces were cut out from the raw tubular films of Run Nos. 15-21 beforethe films were stretched and sealed at one end of the film while thecompressed air was blown in the tubular film from another end thereof,and then the test piece was pulled by hand at the temperature of 30° C.The films of the present invention had the good stability and could bebubbled up, especially the test films of Run Nos. 17 and 20 were easy tostretch.

The films had good properties of the optical character, the lowtemperature shrinkage and the heat shrink tension. The breaking strengthof a commercial polyethylene film which was directly inflated from thedie was only about 2.5 Kg/mm², while the film of the present inventionwas the strong film difficult to break, since it had the moderate degreeof elongation. Especially the wrapping films of Run Nos. 16 and 18 hadhigh dart impact strength and toughness and were superior in thewrapping test and the heat-sealing property.

                                      TABLE 7                                     __________________________________________________________________________                             (weight part)                                                                 Run No.                                              No.                      15 16 17                                                                              18 19                                                                              20 21                                                                              22                                                                              23                               __________________________________________________________________________    a.sub.2                                                                          EVA                              80                                                                              75 80  80                               a.sub.3                                                                          EVA                   80      60                                           a.sub.4                                                                          EVA                      70 80                                                (Melt index: 1.5, vinylacetate                                                group content: 20% by weight)                                              b.sub.3                                                                          Ethylene-α-olefin elastomer                                                                   20 30 20                                                                              40 20                                                                              25   80                                                                              20                               b.sub.4                                                                          Ethylene-α-olefin copolymer (EPM)                                       (α-olefin is propylene, α-olefin                                                                        20                                      group content: 42 mol %, density: 0.87 g/cm.sup.3,                            Vicat softening point: less than 30° C.)                            c.sub.3                                                                          Crystalline PP        18    30   10   25                                                                              20                                    (Melt index: 0.8, ethylene                                                    group content: 6% by weight)                                               c.sub.4                                                                          HDPE                                                                          (Melt index: 0.8, density: 0.960 g/cm.sup.3 ;                                                          20   60                                              modified buten-1 group content: 0.6 mol %)                                 c.sub.5                                                                          Polybutene-1                                                                  (Melt index: 0.4, density 0.913 g/cm.sup.3)                                                                    30                                        c.sub.6                                                                          Polybutene-1                                                                  (Melt index: 1.0, density: 0.908 g/cm.sup.3,                                                                     70                                         modified ethylene group content:                                              8% by weight)                                                                       Dose (Mrad)     5  7  --                                                                              10 --                                                                              5  --                                                                              --                                                                              --                                        Gel %           4  23 --                                                                              24 --                                                                              5  --                                                                              --                                                                              --                                        MI              0.08                                                                             less less 0.09                                                                than than                                                                     0.05 0.05                                         __________________________________________________________________________

                                      TABLE 8                                     __________________________________________________________________________                    Run No.                                                       Property        Unit 15  16  17  18  19  20  21  22  23                       __________________________________________________________________________    Haze            %    0.6 0.5 0.9 0.8 0.6 0.7 1.2 1.5 1.0                      Gloss (20°)                                                                            --   157 162 143 150 155 149 138 140 160                           Temperature at                                                                           °C.                                                                         52  55  56  60  57  61  59  59  56                            20% shrinkage                                                            Thermal                                                                            Maximum shrinkage                                                                        %    78  78  76  74  72  75  74  74  76                       property                                                                           Maximum shrink                                                                           g/mm.sup.2                                                                         230 240 220 230 185 160 190 140 150                           tension                                                                       Temperature at peak                                                                      °C.                                                                         62  75  68  77  70  72  70  69  70                       Tensile strength at break                                                                     Kg/mm.sup.2                                                                        13.6                                                                              18.3                                                                              12.8                                                                              16.7                                                                              16.8                                                                              15.2                                                                              10.2                                                                              9.5 14.8                     Elongation at break                                                                           %    230 195 197 210 170 165 185 185 175                      Dart impact strength                                                                          Kg . cm                                                                            36  48  35  43  31  32  26  25  34                       __________________________________________________________________________

EXAMPLE 5

The raw tubular film 150 mm in diameter, 500μ in thickness andpartiality of ±1.5% in thickness was extruded using the composition andcondition of Run No. 4 and Example 2 and stretched at 50° C. to obtainthe uniform film 45μ in thickness. Even if the thickness of the finishedfilm was thick, the stretch was stably accomplished. The characteristicproperty of the film was the Haze of 1.0%, the tensile strength at breakof 13.5 Kg/mm², and the elongation of 185%. The film was superior in theoptical character and the strength and had the temperature of 60° C. at20% shrinkage and the maximum shrink tension of 230 g/mm², until now, asmentioned above, the directly blown LDPE film had been used in thethicker shrink film in the market (curve 4 in FIGS. 1 and 2). The filmhad less heat shrinkage at the low temperature side and the relativehigh shrinking temperature. The film had high shrinking temperature of117° C. at 20% shrinkage and exceedingly low shrink tension of 5 g/mm²whereby the use was very limited. The thick film was the useful one inthe industrial application.

In the practical test of wrapping the wood, as the result, the speedyshrink-wrapping could be accomplished with the fine wrapping finishhaving no wrinkling, while the uncrosslinked low density commercialpolyethylene film was required higher temperature and longer time forthe heat-shrinkage and created the wrinklings on the surface of thewrapping film and the partial devitrification of the film. Theunsatisfactory result was obtained. If the temperature was raised toaccelerate the wrapping, the temperature reached to the melting point ofthe film before the film was uniformly and sufficiently heated therebydissolving the most part of the film and transferring heat to the goods.

When the film of the present invention was stabilized by heat-treatingat the desired temperature and heat-setting, the film having the gooddimensional stability was obtained at the relatively high temperature offor example about 80° C. This shrinking film was not only limited to thespecific use but also be applicable for the generic wrapping, theagricultural and the industrial uses.

EXAMPLE 6

Seventy weight parts of LDPE (a₅) (the melt index; 0.3, the density;0.917 g/cm³), 30 weight parts of ethylene-α-olefine copolymer (b₁)(referred to above) and 15 weight parts of the crystalline PP (c₁) wereextruded according to the process of the Example 1 to obtain the rawtubular film (Run No. 24). As this film was apt to break in stretching,the film was crosslinked by radiating the high energy ray of 10 mrad soas to have the melt index of less than 0.05 and contain about 40% byweight of gel and then stretched at the stretching temperature of 65° C.thereby obtaining the film 16μ in thickness. This film had the followingproperties; Haze; 1.8%, Temperature at 20% shrinkage; 70° C., Heatshrink tension; 210 g/mm², Tensile strength; 8.5 Kg/mm², Elongation:155%; Dart impact strength: 22 Kg.cm.

EXAMPLE 7

The stable stretching was carried out under the same condition to thoseof Run No. 2, Example 1, using the ethylene-ethyl acrylate copolymer(a₆) (the ethyl acrylate unit content: 10 weight %, the melt index: 2.5)(Run No. 25) or the ethylene-methyl methacrylate copolymer (a₇) (themethyl methaacrylate unit content: 15 weight %, the melt index: 2.0)(Run No. 26) instead of EVA (Run No. 2). This films had the followingproperties respectively: Haze; 1.4%, 1.7%. Tensile strength: 8.9 Kg/mm²,9.8 Kg/mm². Elongation: 200%, 180%, Dart impact strength 26 Kg.cm,Temperature at 20% shrinkage; 60° C., 65° C., Shrink tension: 140 g/mm²,165 g/mm². The gel % was 12, 15 weight % by radiating the high energyray of 7.5 Mrad.

COMPARATIVE EXAMPLE 1

The raw tubular films having the compositions of Table 9 were extrudedfrom the die and quenched to obtain the extruded film 100 mm indiameter, 200μ in thickness and partiality of ±1.8% in thickness. Thesaid film was stretched under the same processing conditions as those ofExample 1.

                  TABLE 9                                                         ______________________________________                                              Comparative                                                                   example                                                                 Compo-                                                                              Run No.                                                                 sition                                                                              1      2      3    4    5    6    7    8   9   10                       ______________________________________                                        a.sub.2                                                                             100                                    80                               a.sub.3      100                                                              b.sub.2                                 100      20  20                       c.sub.1             100                      20  70                           c.sub.3                  100                         70                       c.sub.4                       100                                             c.sub.5                            100                                        ______________________________________                                         Note:                                                                         Unit is based on the weight part.                                        

The films of the comparative sample Run Nos. 1 and 2 could not becontinuously stretched at all under the temperatures of 40° C., 50° C.,60° C., 70° C., 80° C. and 90° C. respectively and were caused breakagewhen air was blown in the tube. The batch test of this film could not becarried out. These raw films were difficult to continuously stretchwithout heating the films at the temperature of more than 140° C. Thesefilms had Haze of 4.1% and 5.1%, the breaking strength of 2.5 and 2.8Kg/cm², the elongation of 580% and 450% respctively. These films had notthe low temperature shrinkage, and the shrink tension was almost null.These raw films were similar one with the film manufactured from the dieby direct inflation and inflating while cooling by air. These raw filmscontained the gel of 38, 21% by weight respectively when they wereradiated with the energy ray (hereinafter it is called E-treatment forshort). These films had a similar tendency with the above example.

The raw film having the composition of Comparative Example Run No. 3could not be inflated like the bubble at all since it was causedbreakage at the temperature not more than 140° C. This raw film couldnot be stretched in the continuous or batch process. This raw film wasdifferent from that of the present invention. This raw film was somewhatinflated at the temperature more than 140° C. and it was apt to causebreakage immediately after the inflation. This film had the badtransparence having Haze of 5.2% and could not carry out the lowtemperature shrinkage. This film did not contain the gel even if theE-treatment was carried out. The film was almost the same to the filmthat the E-treatment was not carried out.

The raw film having the composition of Comparative Example Run No. 4 hadlow stretching temperature than that of Comparative Example Run No. 3.This film had the exceedingly unstable stretching character and couldnot carry out the low temperature shrinkage and was inferior in thestrength and had Haze of 4.7% and the temperature of 117° C. at 20%shrinkage.

The raw film having the composition of Comparative Example Run No. 5could not be inflated at all at the temperature of not more than themelting point (135° C.) and was caused breakage in the continuous orbatch process. The film which was inflated at the higher temperature of150° C. in the same manner to the conventional direct inflation processcould not be highly oriented and had the bad optical character. Thisfilm was opaque and had Haze of 20%.

The film having the composition of Comparative Example Run No. 6 hadhigh Haze and was opaque as the film of Comparative Example Run No. 5.

The film having the composition of Comparative Example Run No. 7 hadelasticity as rubber. This raw film was somewhat inflated at the lowtemperature of not more than 90° C. However it was caused breakage andshrinkage of bubble. The satisfactory film could not be obtained. As theraw tubular film occurred blocking at the high temperature of about 140°C., the said film could not be stretched at the high temperature.

The raw films having the compositions of Comparative Example Run Nos. 8,9 and 10 were caused breakage and could not form the film at lowtemperatures even if the batch and continuous processes were carriedout. At high temperatures of the melting point of the crystalline PP(165° C.) (c₁) or at the temperature somewhat less than the saidtemperature, namely the temperatures of 140° C. (Comparative Example RunNo. 9) and 133° C. (Comparative Example Run No. 10), the films wereunstable and caused breakage immediately after the inflation. Howeverthe films could be hardly stretched. These films had Haze of 4.6% and3.9%, the temperature of 109° C. and 104° C. at 20% shrinkagerespectively and had not the low shrinkage temperature as the raw filmcarried out the E-treatment of Example 1. The tensile strength at breakwas 5.1 Kg/mm² and 6.2 Kg/mm² respectively and it was not so high level.

The film of the Comparative Example 1, Run No. 11 having the compositioncomposed of 70 weight parts of the crystalline PP (c₁) and 30 weightparts of LDPE (the melt index; 1.5, the density; 0.918 g/cm³) wasinstable at the temperature of 140°-160° C. near to the melting point(165° C.) of the crystalline PP and had high Haze of 5.6%. Of course,this raw film had the low oriented film not having the low temperatureshrinkage and having the rough surface of Haze of 18.6% at thetemperature of not less than 165° C. This film could not be inflated atthe temperature of not more than 140° C. since the bubble was causedbreakage.

The raw film of Comparative Example Run No. 12 composed of 80 weightparts of the crystalline PP (c₁), 10 weight parts of LDPE (the meltindex: 1.5, the density: 0.918 g/cm³) and 10 weight parts of theethylene-α-olefin copolymer elastomer (b₂) was unsatisfactory as inComparative Example Run No. 11.

COMPARATIVE EXAMPLE 2

Two raw tubular films as in Example 1 were heated to 115° C. and 150° C.respectively and then stretched, one of which was the film 200μ inthickness manufactured according to the composition and the process ofExample 1 without the E-treatment, another of which was the film 200μ inthickness manufactured according to the composition and process ofExample 1 with the E-treatment. The satisfactory stretched film couldnot be manufactured from these raw films, since said film was brittleand was caused breakage when the stretching was carried out at 115° C.by blowing the compressed air within the raw tubular film. This film waswhitish and opaque in appearance. While the satisfactory stretchingcould be accomplished at 150° C. and these raw films were inflated to 3times in the vertical direction and 4.4 times in the lateral direction.The resulted films had the following properties respectively: Haze 3.8%,3.6%. Temperature at 20% shrinkage: 107° C., 106° C., Shrink tension: 3,10 g/mm², Breaking strength: 2.9 Kg/mm², 3.5 Kg/mm². Elongation: 520%,480%. The film had not the low temperature shrinking property and hadthe bad optical character and the low breaking strength and the shrinktension of almost null. The said films were different from the film ofthe present invention in the use.

These raw tubular films were caused breakage when the film werestretched to 6 times in the vertical direction only at 60° C. and thestretching elongation was returned. The film had the bad opticalcharacter and was lack of uniformity. The raw tubular film was cut offand heated at the temperature of 40°-90° C. and heated at thetemperature of 40°-90° C. and stretched to 2 times in the vertical andlateral directions by the tenter for the biaxial stretching use. Thestretched film was lack of uniformity in thickness and caused breakage.Thus this film could not be satisfactorily stretched. This film wasbrittle and easily broken at the temperature of about 100°-110° C. Therewas merely obtained the film having the bad optical character (Haze:11.5%) at the temperature of 140° C.

COMPARATIVE EXAMPLE 3

Two raw tubular films containing the gel of 62% and 65% respectivelywere manufactured from LDPE (the melt index: 1.5, the density: 0.918g/cm³) only and EVA (a₁) only by radiating the energy ray of 15 Mradaccording to the process of Example 1. The resulted raw films wereheated to the temperature of 150° C. and then stretched to 4.0 times inthe vertical direction and 6.0 times in the lateral direction to obtainthe film 16μ in thickness. These films had the following propertiesrespectively Haze: 2.5%, 2.1%. Temperature at 20% shrinkage: 97° C., 87°C. Shrink tension: 115 g/mm², 95 g/mm². Tensile strength at breakage:6.2 Kg/mm², 8.3 Kg/mm². Elongation: 80%, 95%. Dart impact strength: 7.2Kg.cm, 10.3 Kg.cm.

These films were difficult to be heat-sealed and the temperature rangefor heat-sealing was narrow and the high temperature side and weredifficult to melt-cut with a heating wire at the time of wrapping.

EXAMPLE 8

The compositions composed of the components as shown in Table 10 exceptRun No. 31 were plasticized and kneaded at the maximum temperature ofcylinder part of 260° C. by the mixing head type screw 45 mm in diameter(L/D=44) and pelletized to form pellet. The composition of Run No. 31,Table 10 was manufactured by kneading PP (c₂) and EPM (b₄) into Banburymixer to make the master batch pellet and diluting the resultant withother components (a₁). The compositions were extruded through anextruder 45 mm in diameter (L/D-37) fitted with T-type die which had aslit 1 mm in thickness and 40 cm in width, while extruding a liquidadditive was injected into the rear part of cylinder under pressure. Themelted polymer compositions extruded from the die were introduced intowater to form raw tubular films 100μ in thickness. One of the resultedfilms was treated with the radiation of energy ray and the other wastreated. They were examined for comparison. The results were shown inTable 11.

                  TABLE 10                                                        ______________________________________                                                Run No.                                                               Composition                                                                             27      28       29    30     31                                    ______________________________________                                        a.sub.1   85      85             80     85                                    b.sub.4                                 15                                    b.sub.1   15      15             20                                           b.sub.2                    80                                                 c.sub.1                    20                                                 c.sub.2   20                     80     20                                    Dose (Mrad)                                                                             --      7        --    10     5                                     Gel %     --      33       --    8      20                                                      less                  less                                  M I               than           0.07   than                                                    0.05                  0.05                                  ______________________________________                                    

The films had tensile strength, impact strength, heat sealing strengthand tear strength in high level. The films had wide temperature aptitudefor heat-sealing and good sealing strength. Especially, the film of RunNo. 30, Table 10 was treated by radiating energy ray of 10 Mrad.However, the film had wide temperature aptitude for sealing and goodsealing strength. The films of No. 27, No. 30, Table 10 had goodstifness and were superior as the wrapping films.

                  TABLE 11                                                        ______________________________________                                                   Run No.                                                            Property     27      28      29    30    31                                   ______________________________________                                        Haze (%)     1.8     1.5     1.6   2.5   2.2                                  Tensile strength at                                                           break (Kg/mm.sup.2)                                                                        3.5     3.3     3.0   3.8   3.4                                  Elongation (%)                                                                             820     840     730   670   700                                  Dart impact strength                                                          (Kg . cm)    73      64      54    80    66                                   Heat sealing strength                                                         (Kg/15mm width)                                                                            2.1     1.8     1.5   2.3   1.7                                  ______________________________________                                    

EXAMPLE 9

The compositions of Run No. 27, Table 10 and the vinylidenechloride-vinylchloride copolymer (hereinafter referred to as PVDC) wereextruded using an annular die having three layer structures with threeextruders and then inflated by the water cooling type inflation processto obtain co-extrusion film composed of a film of the composition RunNo. 27, 25μ in thickness as the outer layer, a film of the compositionRun No. 27, 30μ in thickness as the inner layer and a film of thecomposition PVDC 10μ in thickness as the middle layer. The film has thefollowing properties: Haze--2.1%, Tensile strength at break--5.1(kg/mm²), Elongation--460 (%), Dart impact strength--78 (Kg.cm),Heat-sealing strength--2.2 (Kg/15 mm width). The inflation process couldbe carried out very stably and had a less problem. On the other hand,when (a₁) alone was used instead of the composition of Run No. 27 forthe outer and inner layers, the film prepared suffered surging and sothe inflation process was instable.

What is claimed is:
 1. A cold drawn film having a tensile strength ofnot less than 5.0 kg/mm² and a haze of not more than 4.0% which filmcomprises a homogeneous blend of the combination of components (B)+(C)wherein the components of the composition are in amounts such as tosatisfy 0.90≧B/(B+C)≧0.30 in terms of weight ratio;(B) is athermoplastic elastomer having a density of not more than 0.91 g/cm³ andmade of an ethylene-α-olefin copolymer, and (C) is at least one selectedfrom the group consisting of crystalline polypropylene, high-densitypolyethylene and crystalline polybutene-1.
 2. The film according toclaim 1, wherein the ethylene-α-olefin copolymer as the component (B)has an ethylene group content of not more than 90 mol% and not less than20 mol%.
 3. The film according to claim 1, wherein the ethylene-α-olefincopolymer as the component (B) has an ethylene group content of not morethan 90 mol% and not less than 40 mol%.
 4. The film according to claim1, wherein the elastomer as the component (B) is a non-rigid copolymerhaving a Vicat softening point of not more than 80° C. and a degree ofcrystallization of not more than 30%, wherein the α-olefin componentcontained therein is at least one member selected from the groupconsisting of α-olefins having from 3 to 12 carbon atoms.
 5. The filmaccording to claim 1, wherein the elastomer as the component (B) is arandom copolymer wherein the α-olefin component contained therein isselected from the group consisting of propylene and butene-1.
 6. Thefilm according to claim 1, wherein the ethylene-α-olefin copolymer asthe component (B) has a polyene copolymerized in addition to the maincomponents of ethylene and α-olefin.
 7. The film according to claim 6,wherein the polyene contains not more than 5 mol% of a non-conjugatediene selested from the group consisting of hexadiene and norbornenederivatives.
 8. The film according to claim 1, wherein the component (C)is a rigid polymer having a Vicat softening point of not less than 100°C.
 9. The film according to claim 1, wherein the component (C) is eithera crystalline polypropylene or a crystalline copolymer of propylene withethylene contained in an amount of not more than 10 mol%.
 10. The filmaccording to claim 1, wherein the components of the composition are inamounts such as to satisfy 0.87≧B/(B+C)≧0.40 in terms of weight ratio.11. The film according to claim 1, wherein the composition whichconstitutes the film has an insoluble gel content of from 60 to 0% byweight in boiling xylene and a melt index of not more than
 10. 12. Thefilm according to claim 1, wherein the composition which constitutes thefilm has an insoluble gel content of from 50 to 0% by weight in boilingxylene and a melt index of not more than
 5. 13. The film according toclaim 1, wherein the composition which constitutes the film has beencrosslinked and has an insoluble gel content of from 40 to 0% by weightin boiling xylene and a melt index of not more than 0.2.
 14. The filmaccording to claim 1, wherein the film has a heat shrink tension of notless than 50 g/mm².
 15. The film according to claim 1, wherein thetemperature at which the film exhibits a heat shrinkage of 20% is notmore than 85° C.
 16. The film according to claim 1, wherein thetemperature at which the film exhibits a heat shrinkage of 20% is notmore than 75° C.
 17. The film according to claim 1, wherein the film hasa Haze of not more than 3.0%.